The pressure at which typical gas distribution systems supply gas may vary according to the demands placed on the system, the climate, the source of supply, and/or other factors. However, most end-user facilities equipped with gas appliances such as furnaces, ovens, etc., require the gas to be delivered in accordance with a predetermined pressure, and at or below a maximum capacity of a gas regulator. Therefore, gas regulators are implemented into these distribution systems to ensure that the delivered gas meets the requirements of the end-user facilities. Conventional gas regulators generally include a closed-loop control actuator for sensing and controlling the pressure of the delivered gas.
In addition to a closed loop control, some conventional gas regulators include a balanced trim to improve the reaction of the gas regulator to variations in the downstream pressure. The balanced trim is adapted to reduce the influence of the upstream pressure on the performance of the gas regulator. The upstream pressure is placed in fluid communication with a balancing diaphragm to apply a force to the control element of the gas regulator in the opposite direction as the force of the downstream pressure. Accordingly, as the upstream pressure varies, a corresponding force is applied to balance the force created by the upstream pressure as described further below so that the gas regulator acts in response to the downstream pressure only.
In conventional regulators having a balanced trim, a portion of the fluid flowing through the gas regulators may travel through channels that are longitudinally disposed within the control element, and the channels open to a balancing cavity that is at least partially defined by the balancing diaphragm. Such a configuration allows for high flow capacity at low inlet pressures. However, as the valve opens, the inlet pressure bearing on the balancing diaphragm does not remain constant. More specifically, the sensing pressure reduces as the valve opens, resulting in “droop” and instability in the gas regulator.